Biomedical subjects

Vsevolod A Livshits

Publications and source records attributed to Vsevolod A Livshits.

4 recordsLinked to original sources

PubMed2006

Oxygen profiles in membranes.

Transmembrane profiles of molecular oxygen in lipid bilayers are not only significant for membrane physiology and pathology, but also are essential to the determination of membrane protein structure by site-directed spin labeling. Oxygen profiles obtained with spin-labeled lipid chains have a Boltzmann sigmoidal dependence on the depth into each lipid leaflet, which represents a two-compartment distribution between outer and inner regions of the membrane, with a transfer free energy that depends linearly on distance from the dividing planes. Transmembrane profiles for intramembrane polarity, and for water penetration into the membrane, have an identical form, but are of the reverse sign. Comparison with recently published oxygen profiles from a site-specifically spin-labeled alpha-helical transmembrane peptide validates the use of spin-labeled lipids for all these profiles and provides the necessary bridge to generate the full bilayer from a single lipid leaflet.

Biophysics↗

PubMed2005

High-field spin-label EPR of lipid membranes.

High-field EPR of spin-labelled lipid chains has proved to be an extremely productive means for biophysical investigations of phospholipid bilayer membranes. Results on the following three topics are reviewed: 1. Non-axial ordering of lipid chains in cholesterol-containing membranes; 2. Transmembrane polarity profiles and water penetration in lipid membranes; 3. Role of HF-EPR in multi-frequency spectral simulations to investigate lipid-chain dynamics in membranes. These results are obtained from phosphatidylcholine spin probes with the nitroxide systematically stepped down the sn-2 chain, in fully hydrated bilayer membranes of dimyristoyl phosphatidylcholine (DMPC)-containing cholesterol.

Cholesterol↗

PubMed2003

Oxygen permeation profile in lipid membranes: comparison with transmembrane polarity profile.

Permeation of oxygen into membranes is relevant not only to physiological function, but also to depth determinations in membranes by site-directed spin labeling. Spin-lattice (T(1)) relaxation enhancements by air or molecular oxygen were determined for phosphatidylcholines spin labeled at positions (n = 4-14, 16) of the sn-2 chain in fluid membranes of dimyristoyl phosphatidylcholine, by using nonlinear continuous-wave electron paramagnetic resonance (EPR). Both progressive saturation and out-of-phase continuous-wave EPR measurements yield similar oxygen permeation profiles. With pure oxygen, the T(2)-relaxation enhancements determined from homogeneous linewidths of the linear EPR spectra are equal to the T(1)-relaxation enhancements determined by nonlinear EPR. This confirms that both relaxation enhancements occur by Heisenberg exchange, which requires direct contact between oxygen and spin label. Oxygen concentrates in the hydrophobic interior of phospholipid bilayer membranes with a sigmoidal permeation profile that is the inverse of the polarity profile established earlier for these spin-labeled lipids. The shape of the oxygen permeation profile in fluid lipid membranes is controlled partly by the penetration of water, via the transmembrane polarity profile. At the protein interface of the KcsA ion channel, the oxygen profile is more diffuse than that in fluid lipid bilayers.

Anisotropy↗

PubMed2002

High-field electron spin resonance of spin labels in membranes.

High-field electron spin resonance (ESR) spectroscopy is currently undergoing rapid development. This considerably increases the versatility of spin labelling which, at conventional field strengths, is already well established as a powerful physical technique in membrane biology. Among the unique advantages offered by high-field spectroscopy, particularly for spin-labelled lipids, are sensitivity to non-axial rotation and lateral ordering, a better orientational selection, an extended application to rotational dynamics, and an enhanced sensitivity to environmental polarity. These areas are treated in some depth, along with a detailed consideration of recent developments in the investigation of transmembrane polarity profiles.

Animals↗